Recently, a compact and thin-type image pickup apparatus has come to be mounted on a mobile terminal representing a compact and thin-type electronic hardware such as a cell phone and PDA (Personal Digital Assistant). Information such as voice information and image information is transmitted mutually between such the mobile terminal and, for example, an electronic device at a remote location.
As image pickup elements used for these image pickup apparatuses, a solid-state image pickup element such as an image sensor of a CCD (Charge Coupled Device) type and an image sensor of a CMOS (Complimentary Metal-Oxide Semiconductor) type has been used. In recent years, as a lens tor forming an image of a photographic subject on the image pickup element, a lens made of resin that is suitable for mass production has come to be used for further cost reduction.
As such the image pickup lens, especially as an image pickup lens used for an image pickup apparatus (so-called a camera module) housed in a mobile terminal, an optical system of a three-element structure including three plastic lenses and an optical system of a three-element structure including one glass lens and two plastic lenses are widely known. However, demands of further compactness and mass productivity for these image pickup lenses are difficult to be compatible because of their technical limits.
As one of methods to solve the above problem, there has been proposed a replica method in Patent Literature 1. A replica method is a method to form plural lenses (lens elements) on one lens plate (water) simultaneously. Patent Literature 1 discloses an image pickup lens including a junction-type complex lens (lens block) made by the replica method. Patent Literatures 2 to 5 also disclose image pickup lenses each including the lens block.
Patent Literature 1: JP-A No. 2006-323365
Patent Literature 2: JP-B No. 3929479
Patent Literature 3: JP-B No. 3976781
Patent Literature 4: JP-B No. 3946245
Patent Literature 5: JP-B No. 3976782